GENERAL NOTES ON THE CLIMATE. 



569 



tions for August give as the mean per-centage a proportion of saturation but 31 for the hour of 

 7 a. m., and but 20 for that of 2 p. m. That of 9 p. m. is 48, and the mean 33, against a mean 

 of near 75, or an average in the Mississippi valley and the Atlantic States. The calculation in 

 detail would give very low proportions of atmospheric moisture in many cases ; and though 

 this detail is the only accurate mode of obtaining these proportions, the measures here given are 

 a near approximation. 



The quantity of rain is quite imperfectly observed in the record at Fort Benton for several 

 months. The amount is apparently small for the year, the winter and spring having evidently 

 the greatest quantity, and each near five inches. The rains not measured in summer are not 

 noted as profuse in any case; and the distribution seems to partake somewhat of that peculiar to 

 the Pacific climates, which have least in summer. On the plains, the greatest quantities are in 

 spring, and other seasons are often quite without rain. The strong southwest winds, with the 

 high temperature and barometric oscillations then noted at Fort Benton in the winter months, 

 prove a connexion to exist with the Pacific climates which does not appear at any other point of 

 the plains. In these cases the precipitation is doubtless profuse, in rain or snow, on the mount 

 ains of this vicinity. 



The barometric oscillations at Fort Benton and St. Mary s are also quite conformable and 

 identical with each oiher when projected in curves. They exhibit marked movements in some 

 instances quite sudden, and of great range in the winter months, and connect the attendant 

 storms beyond a doubt, as belonging to similar climates at this season. 



The record at St. Mary s valley requires less analysis and comparison, to illustrate its relation 

 to known climates. The position is elevated nearly a thousand feet above Fort Benton, (3412.5 

 feet above the sea,) yet its winter climate is equally mild, and the extremes at that season not more 

 severe. In summer, however, the low temperatures of the Pacific coast are felt, and extremes 

 occur much greater than those at Fort Benton. April has a mean temperature 6.5 degrees lower 

 at Cantonment Stevens., and May 2.5 degrees. In May there is snow on the 7th, as at Fort 

 Benton; and on the 28th snow again, two inches in depth, and rains; none of which appear at 

 Fort Benton. 



In July snow fell on the 6th in small quantity. In the frequent rains of the summer months 

 on the mountains of the vicinity, if not at the post, the sudden changes of temperature and of 

 wind peculiar to mountain regions appear characteristic, and to distinguish the climate here at 

 that season from that of the plains east of the mountains, as well as those towards the Pacific. 



The quantity of rain is not measured at this post for any part of the period of observation. 

 Rains are noted frequently in the remarks, and the number of days of rain and snow may be 

 given here, and in comparison with Fort Benton : 



T2/ 



